FORMATION AND THERMAL-STABILITY OF ALUMINUM NANOPARTICLES SYNTHESIZEDVIA YTTRIUM ION-IMPLANTATION INTO SAPPHIRE

Yttrium ion implantation of <11(2)over bar 3> alumina resulted in the formation of metallic aluminium-yttrium, face centred cubic (<partial derivative (0)> = 0.41 nm) spherical nanocrystals (similar to 12 nm in diameter) embedded in an amorphous matrix. A fluence of 5 x 10(16) Y (+)/cm(2) implanted at ambient temperature and accelerating energies o f 150 or 170 keV yielded this result. Crystalline nanoparticles were n ot present in the amorphous matrix for implantations done with identic al conditions but lower energy (100 keV). Substrates implanted at 150 keV were annealed in laboratory air for times ranging from 20 to 90 mi n and temperatures ranging from 1000 to 1400 degrees C. A clear progre ssion of morphologies resulted from these annealing treatments. A 1000 degrees C, 90 min anneal produced similar to 13% recrystallization of the amorphous region and induced the formation of crystallites of a m etastable Y-Al alloy. An 1100 degrees C, 90 m in anneal demonstrated s imilar to 40% recrystallization of the amorphous region, accompanied b y the formation of partially aligned internal grains of Y2O3. Electron diffraction shows that the Y-Al alloy crystallites which formed in th e 1000 degrees C anneal are also present at 1100 degrees C. A highest temperature anneal of 1400 degrees C, 60 min induced essentially compl ete recrystallization of the amorphous phase, the dissolution of the m etastable Y-Al alloy, the retention of the internal yttria grains, and the formation of partially oriented external grains of yttria resulti ng from the segregation of yttrium to the substrate surface.